An assessment of the iodine status and the correlation between iodine nutrition and thyroid function during pregnancy in an iodine sufficient area

Abstract

Background: Iodine as a micronutrient is mandatory for thyroid hormone production and inadequate iodine intakes during pregnancy may result in varying degrees of hypothyroidism affecting pregnancy outcomes adversely. The aim of this study was to evaluate nutritional status and its effects on thyroid function in pregnant women during all trimesters of pregnancy.

Subjects/methods: In this cohort study, we assessed a total of 203 pregnant women in the first trimester of pregnancy and followed them in the second and third trimesters. They were divided into two groups, group I with urinary iodine excretion (UIE) < 150 μg/l, and group II with UIE ≥ 150 μg/l. Serum samples from women were assayed for levels of total T4, T3, FT4I and thyroid-stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb) only once in each trimester. Urinary iodine concentration was measured three times and the median was considered as UIE in the first trimester, but it was measured only once in the second and third trimesters.

Results: The median inter quartile ranges of urinary iodine were 218 (150-276) μg/l, 160 (106-260) μg/l and 145 (88-225) μg/l in the three trimesters of pregnancy, respectively; UIE<150 was observed in 48 (24.1%), 90 (44.8%) and 103 (52.3%) of pregnant women in the three trimesters of pregnancy, respectively. The median (range) of TSH was 1.7 (0.9-2.7) mIU/l, 1.9(1.2-2.7) mIU/l and 1.8 (1.1-2.8) mIU/l in the three trimesters of pregnancy, respectively. There was no correlation between UIE, TSH, TT4, FT4I, T3 and TPOAb in the first and second trimesters, but there was a weak correlation between UIE, TSH, T3 and TgAb in the third trimester.

Conclusion: In our cohort of pregnant women the iodine intakes were sufficient, and no correlation between urinary iodine concentration and thyroid function tests was found.